Potential Head Separation?

[kyshootnman]

I have been loading for around 5 years, and this is the first time I've saw signs such as this on brass. I have had necks split in the past, but never saw this ring. The case grew about 0.005" below this ring and when I cut the case open, it does have an indention. My question is, does this appear to be a result of pressure, headspace, or what are the other culprits? This did not appear until I ran some 142 SMK's in my 260 at 42.9 H4350. I have been running 140 Amax at 42.8 with no issues. I measured the OAL with each bullet, and was 0.010" off the lands. The brass is Winchester 7mm-08 necked down. This was the third firing on this brass. Do the 142's really create this much more pressure? Thanks in advance.

 

[roggom]

Combination of both, get a Wilson case gage, RCBS precision mic or other to measure the shoulder bump. I like the RCBS as it has the saami spec at zero.

Did your 140's have significant black soot at the necks post firing?

 

[kyshootnman]

I do use a Wilson case gage, and there is some suit around the necks. I was necksizing these cases only, and the OAL of the brass was within spec.

 

[agbm]

What does the black soot mean around the case neck, been getting some but all I'm shooting is factory federal GMM ammo?

 

[ChrisGarrett]

It happens. These 7RM cases had probably 5-6 cycles on them and were stuff I used when I first started reloading and didn't properly grasp the benefits of accurate case sizing.

Get yourself the Hornady/Stoney Point headspace gage set and set all of your bottleneck dies up properly for your particular chambers.

Soot around the necks can be normal. It's gas blow-back. You might want to let your necks grow a little longer, as that creates a better gas seal. Go in small increments.

Chris

 

[roggom]

You can use the wilson gage to check bump, as long as the neck is not protruding from the bottom. You can use a caliper to measure a fired case, then put the sized case and measure. You are looking for a .002 difference.

Sure the Wilson can be used as a quick and easy go, no go for case length as the rim will stick above the line or the neck will protrude a little. The higher portion of the die is .005 higher than the lower portion.


As Chris stated the black soot can be had even if the load is correct, it is just that some rifles have longer throats, some loads are lighter, or the headspace can be on the longer side. The soot is more prevalent with excessive HS, being the chamber, or the cases being sized to much.

 

[kyshootnman]

How could it be my sizing method when I was neck sizing only? The rounds were chambering fine with no force. I do have rcbs mic sets for other calibers but have not saw one for 260.

 

[turbo54]

How could it be my sizing method when I was neck sizing only? The rounds were chambering fine with no force. I do have rcbs mic sets for other calibers but have not saw one for 260.

Does not compute...

CHSs are a product of either a chamber with too much headspace, or repeated Oversizing of brass.

 

[ChrisGarrett]

How could it be my sizing method when I was neck sizing only? The rounds were chambering fine with no force. I do have rcbs mic sets for other calibers but have not saw one for 260.

I was getting ready to size some 338LM Norma/Lapua brass with a solid 12+ cycles on them. I got my H/SP headspace gage out and got a relative reading for the Normas, which were giving me hard bolt lifts on a moderate load. Let's just say they were roughly .013"-.014". I figured I'd check some new Lapua brass that is virgin and see what the factory is doing, as I didn't have the HS gage way back when.

Well, .004" on the four, or five, that I measured. Assuming that the chamber itself is a snug .012", then that's .008" of strectching that the Norma cases 'probably' went through on the first cycle.

You can separate heads on a single firing, although it's rare.

Chris

 

[EXTREMEPREJUDICE]

What you are seeing is the pressure ring developing on the case wall (a little forward of the case head) that expands during firing and since you are only neck sizing it will stays expanded more than the rest of the case. Its diameter increases with the peak pressure of the load. It could be the result of overpressure but not necessarily. What does the primer look like? Are you seeing any ejector marks? It does not look like the ring that forms due to excessive headspace (could be) but you mentioned you are only neck sizing, how far are you bumping the shoulder back? If you are jumping the projectile 0.010 (ten thousands, correct?) is it off the ogive as you refer to OAL (I hope you don't mean the metplat is 0.010 from the lands?) Finally, is this just one single case or has it happend to the entire lot?

 

[kyshootnman]

I'm thinking you have hit it on the head Extreme. This explanation makes the most sense. This lot of cases did not show this sign until I fired them with the 142. I can argue that it's not a headspace issue because it doesn't take 3 firings for the brass to form to the chamber, therefore it's not a result from excess chamber headspace. The primers are not flat nor show any dimpling, no ejector marks, I haven't been bumping the shoulder any because the rounds chamber with no effort. The bullet is 0.010 off the lands from the ogive. I have several other pieces of brass that have been fired in this rifle using 140 smks and 140 amax with no ring such as this. The most any have been fired is three times.

 

[Sniper Uncle]

I'm missing something here. You said you were shooting 42.8 gr powder with a 140gr bullet, then went to a 142gr bullet and went up to 42.9gr powder. I know that the bullet weight change was very small, but the books do say higher weight bullet, lower weight powder charge almost all the time. I don't have a hell of a lot of experience, but I do question that those two small changes should have too much impact on the casings, I was just wondering if I understand the principles here properly. Also, are the marks in question only on the three times fired cases? Did you try a third time on any cases with the 140/42.8 set-up? Did they react the same, or different? If you didn't try them, would you be able to try them?

Forgive my ignorance here if I have missed the whole point, I'm trying to learn myself.

 

[kyshootnman]

42.8 was not the upper node for pressure with the 140's, that's just where I was seeing the best results. I did a ladder test on the 142's, and this ring was present all throughout the loads. I started low and worked up. I have some other 7mm-08 and 243 brass I run in it, and they have been fired 3 times, without showing anything significant. My OAL is 2.875.

 

[Sniper Uncle]

Thanks for the extra info. I was just asking the questions more to learn myself than anything else. Curious to see what you find out in the end. Good luck,

 

[Aimsmall55]

42.8 was not the upper node for pressure with the 140's, that's just where I was seeing the best results. I did a ladder test on the 142's, and this ring was present all throughout the loads. I started low and worked up. I have some other 7mm-08 and 243 brass I run in it, and they have been fired 3 times, without showing anything significant. My OAL is 2.875.

Not to be a smart ass but why are you running 243 and 7-08 brass? Lack of good .260 brass??

 

[kyshootnman]

Not to be a smart ass but why are you running 243 and 7-08 brass? Lack of good .260 brass??

That's just what I have available. I wanted to try each in the gun to see which it likes better.

 

[Aimsmall55]

Got ya.. Completely understand that!

 

[roggom]

How could it be my sizing method when I was neck sizing only? The rounds were chambering fine with no force. I do have rcbs mic sets for other calibers but have not saw one for 260.

Ok , I went back and actually read your whole post. You are using 7mm-08 brass sized to 260. Without any empirical data it is difficult to make a proper assessment. One thing for sure, you know that a case head separation is imminent with your current setup.


As for the bump or resizing, if you were oversizing your brass you would feel absolutely no resistance when chambering the round.

Good luck

 

[kyshootnman]

Camming the bolt doesn't feel out of the ordinary.... I dunno.. Do you think running the brass through the full length die would correct the problem in the future?

 

[Sniper Uncle]

Ok , I went back and actually read your whole post. You are using 7mm-08 brass sized to 260. Without any empirical data it is difficult to make a proper assessment. One thing for sure, you know that a case head separation is imminent with your current setup.


As for the bump or resizing, if you were oversizing your brass you would feel absolutely no resistance when chambering the round.



Good luck

Curious, why do you say that a case head separation is imminent?

 

[roggom]

^^ Because OP opened the case and found case wall indentation. http://www.accurateshooter.com/technical-articles/case-head-separation-cause-diagnosis/ if not imminent a little risky.

It is sort of a tough one without all of the measurements, 7mm-08 to 260 may need to be neck turned (depending on how tight the chamber is ). At this point it is a guessing game.

 

[Win_94]

I wanted to display these cases I have that got some head separation when I forgot I had cleaned my bore and chamber thoroughly, then coated them with oil preservative. I forgot to clean the chamber of oil before shooting. What happened was that the case didn't grip the chamber wall resulting in stretching of the case mainly at the head area.

You can see how each case stretched less as the oil was rubbed off onto the case preceding the next one.
The cartridges were loaded with a trusted mid-level 30-06 load... the line in the center of the case wall, is a minor chamber irregularity.

How many cases were affected? Maybe the chamber or affected case/cases were contaminated with sizing lubricant, water, oil or cleaning solvent?

 

[Sniper Uncle]

^^ Because OP opened the case and found case wall indentation. http://www.accurateshooter.com/technical-articles/case-head-separation-cause-diagnosis/ if not imminent a little risky.

It is sort of a tough one without all of the measurements, 7mm-08 to 260 may need to be neck turned (depending on how tight the chamber is ). At this point it is a guessing game.

Thank you for clarity. I had forgotten the part about his cutting the case....

 

[ChrisGarrett]

I wanted to display these cases I have that got some head separation when I forgot I had cleaned my bore and chamber thoroughly, then coated them with oil preservative. I forgot to clean the chamber of oil before shooting. What happened was that the case didn't grip the chamber wall resulting in stretching of the case mainly at the head area.

You can see how each case stretched less as the oil was rubbed off onto the case preceding the next one.
The cartridges were loaded with a trusted mid-level 30-06 load... the line in the center of the case wall, is a minor chamber irregularity.

How many cases were affected? Maybe the chamber or affected case/cases were contaminated with sizing lubricant, water, oil or cleaning solvent?

You sure that you sized those cases properly, to your chamber?

Just because you have some light lubricant coating your chamber, doesn't mean your cases are going to behave poorly upon ignition. Also, if your headspace is correct, you won't get much stretching, because there's no where for that metal to stretch out to.

Maybe it's the lighting, but your case necks are black, as are your shoulders and that tells me that you've oversized your cases and you're getting gas blow-by, covering them with soot.

Chris

 

[Win_94]

Maybe it's the lighting, but your case necks are black, as are your shoulders and that tells me that you've oversized your cases and you're getting gas blow-by, covering them with soot.

Chris

They have never been full length sized, or cleaned in any way. They have been shot 31 times and the lube accident happened at about the 15th shot mark. The soot comes from a mild load in conjunction with 5 annealings... and yes, the lighting is bad too.

 

[kyshootnman]

Update: I have fired more rounds on the other brass and have no signs of any type on it while using 140 amax. Apparently there is something finicky about 142 smks in my gun. So this ring must have been from over-pressure using the 142's.

 

[sinister]

Sizing with either a full-length or small base die you only want to push shoulders back about .002".

.003" and more and your case walls will stretch and thin on each firing.

Some will say small base sizing is abusing your brass. Pushing the shoulders back .003" or more may be more abusive as the walls thin, contributing to shorter case life.

Thinning from pushing the shoulders back too far:

These cases were deliberately set back .003" to .005" to document stretching and thinning to failure:

 

[Deadshot2]

I have found that in many cases this is an issue of excessive headspace and can start with the very first firing of the case. Follow the die makers instructions of screwing the die in 1/4 turn more than just touching in the Full Length Sizing die and you can start this problem from the get go. Subsequent firings just beat on this groove until the case finally cracks along the line.

A great example of why one should use a case gauge or headspace tool to set up their sizing dies. Remember, the ammo makers only expect a case to last ONE firing. Not dozens of subsequent reloads so a little "short" on the headspace is no big deal to them.

 

[Bluejazz]

All great information, but how do you deal with new brass that already comes fl sized when bought. There is no way to bump the shoulder back .002 until after firing.
So if the stretching starts from the get go, how is this avoidable?

 

[kyshootnman]

As I stated earlier, I'm aware that you only need to set the shoulder back 0.002", but these cases were neck sized only. This eliminates shoulder bump as a possibility all together. I have the appropriate gages and such. Other brass has been fired more times than these cases, and not showing any similar signs. The smk's are just creating more pressure in my chamber.

 

[sinister]

I'm not exactly sure how a neck-sized only case can stretch even farther, pressure or not -- it's been fire-formed to fit the chamber, so there's not much allowance to lengthen.

A Wilson gage will only tell you if a case falls within a min-max range and not whether or not you're nailing shoulder push to only .002". You need something like a Stoney Point/Hornady LNL gage.

If the chamber is deep then you can get case stretching on the fire-forming shot.

When forming the 260 cases from (virgin?) 7-08 did you anneal first and check your base-to-shoulder dimension? Second and third firing (neck-sizing only) without annealing can work-harden the neck and contribute to cracking.

 

[Scooter64]

Thanks. That's good info. I personally have been trying to figure how many firings my winchester and federal 308 case can last so i do not throw then out with life left in them. It's being fired out of my M1A. Today i fired my sixth reloading of the win brass and my third. No sign case head separation. I don't want to be penny wise and pound foolish but i dont want to be wasting my money either.

 

[kyshootnman]

The case neck is not the problem, therefore annealing the neck would have no affect what-so-ever on the issue at hand. Yes, you can use a caliper to measure headspace with a Wilson gage. As far as the case stretching, it would have on the first shot if this was a headspace issue. It doesn't take 3 firings for brass to grow to chamber specs.

 

[sinister]

True, and no argument. The case can, however, stretch and thin on that first firing.

I am interested how you measure headspace using just calipers and the Wilson gage.

 

[Edo1]

If neck sizing only will prevent case head separations, then why does the length of the case grow longer with each firing no matter how it's resized? With each firing on cases like the 308/30-06 with around a 30 degree shoulder, all the brass ahead of the case head flows towards the neck on each firing, causing the case length to grow. Where do you think that growth comes from? The entire case in front of the head flows towards the case mouth due to the high pressure.

 

[kyshootnman]

I was simply stating that the brass hadn't been over-worked due to fl sizing. As long as the case is trimmed to the minimum length you can use calipers to measure with Wilson gage.

 

[Sniper Uncle]

According to Rocky Gibbs, a rough chamber can help cause a case head separation. In your OP, you went up one tenth grain in powder while going up 2 grains in bullet weight. Could this be just enough with a rough chamber to raise the pressure enough where the brass is grabbing the chamber wall harder and the case is stretching near the head instead of sliding back that minute amount???

Kinda shooting in the dark to get intelligent responses of where my thinking is flawed. I'm curious about this issue too.

 

[Edo1]

Has anyone seen a test to show what the real difference on case life is using FL resizing vs neck sizing only? The table from Sinister just shows the results of loading brass using FL resizing. I suspect most are seeing their brass become useless from loose primer pockets before the head separates.

 

[sinister]

Case overall length, as pointed out above, will always grow as the brass flows toward the case mouth (either from firing or re-sizing, especially full-length sizing -- the brass only has one direction to go/flow, and that's towards the case mouth).

Trimming the case back to minimum dimensions keeps the case within the boundaries of the chamber (the neck doesn't extend into the bore, "Pinching the bullet" and raising pressure).

Without an RCBS mic (as the OP pointed out) or some other device on your calipers (a Stoney Point or Hornday LNL, or some kind of comparator to consistently measure base-to-shoulder datum), how are you measuring?

Neck-sizing only/exclusively does not change the base-to-shoulder datum dimension or length, however the brass may eventually stick in the chamber and need an occasional full-length sizing to keep feeding and extraction easier. The frequency of how often you'll want to do it will vary by chamber pressure and brass hardness.

The first firing will determine the case's working length. If the brass had to stretch on the first shot the virgin brass will stretch-to-fit the chamber length. If it's a deep chamber then that's where first thinning will occur. Annealing will help with neck life later (as the neck is work-hardened), but may affect how much/far the the brass in the case walls and shoulder is worked on the fire-form.

The 142 SMK and the 140 A-Max are nominally the same length. The Sierra has a shorter bearing area and ogive. If seated to the same cartridge overall length as the A-Max it may touch the rifling leade sooner. In the OP's case, the bullet may jam into the lands sooner, spiking his pressure up a bit (in the Match King's favor it has a longer boat-tail which may also free up some case space. Add .1 grains more powder (as in his case) and pressures might (or might not) change (bullet seats earlier, plus more fuel).

Do you have a gage to check when your bullet ogives contact the leades, and then adjust from there for a touch fit, jam-fit, or free-jump?

Hodgdon's data states 41.5 to 44.5 of H4350, so your loads are well within min-max charges.

In the graphs I posted the case shoulders were DELIBERATELY pushed back .003-.005 to document case stretch to failure. Neck-sizing only (as benchresters do), or pushing back the shoulders .001-.002 with light-to-moderate charges should extend case life a bunch.

 

[ChrisGarrett]

Has anyone seen a test to show what the real difference on case life is using FL resizing vs neck sizing only? The table from Sinister just shows the results of loading brass using FL resizing. I suspect most are seeing their brass become useless from loose primer pockets before the head separates.

Yeah, I don't worry about it too much either. I'd rather get more cycles, then less, obviously, but brass is a consumable item for me.

I don't know if you could do a valid test because you can't really use the same piece of brass for the study, only brass from the same bag, or box and then happenstance might just prevail.

Why did one of my Norma 338LM's neck split, out of 20, after only two cycles and the other 19 have been going strong for a total of 10 cycles, with nary a problem?

Inquiring minds want to know.

Chris

 

[Sniper Uncle]

Yeah, I don't worry about it too much either. I'd rather get more cycles, then less, obviously, but brass is a consumable item for me.

I don't know if you could do a valid test because you can't really use the same piece of brass for the study, only brass from the same bag, or box and then happenstance might just prevail.

Why did one of my Norma 338LM's neck split, out of 20, after only two cycles and the other 19 have been going strong for a total of 10 cycles, with nary a problem?

Inquiring minds want to know.

Chris

Maybe the factory annealing wasn't quite up to par??? Maybe it got exposed to some chemical or other substance that the others didn't??? Or is it possible that the case neck got dinged worse than the others in shipping and you had to work it a little more to get it straightened out for first use???
Just a few thoughts that came to mind...

 

[milo 2.0]

Maybe the factory annealing wasn't quite up to par??? Maybe it got exposed to some chemical or other substance that the others didn't??? Or is it possible that the case neck got dinged worse than the others in shipping and you had to work it a little more to get it straightened out for first use???
Just a few thoughts that came to mind...

In my experience, when I get a split neck on first or second firing, it's a result of insufficient chamfering. It didn't stand a chance from the start.

 

[ChrisGarrett]

Maybe the factory annealing wasn't quite up to par??? Maybe it got exposed to some chemical or other substance that the others didn't??? Or is it possible that the case neck got dinged worse than the others in shipping and you had to work it a little more to get it straightened out for first use???
Just a few thoughts that came to mind...

Yes, all good supositions, but when you're doing an experiment and drawing conclusions, you'd want to eliminate variables and focus on the parameter that's the center of the experiment, in this example, it's FL sizing vs. Neck sizing and that might be a tough row to hoe.

Chris

 

[sinister]

Not to hijack the thread, Chris, but from what I've read about .338 Lapua brass (especially since Lapua pioneered it and put their name on it), is Lapua's .338 was specifically designed with hard heads/bases (as a result of the way they draw their cases) and the necks and shoulders are typically softer -- if you look at virgin Lapua-brand .338 LM cases they're nicely annealed out of the shipping box.

 

[Edo1]

In the graphs I posted the case shoulders were DELIBERATELY pushed back .003-.005 to document case stretch to failure. Neck-sizing only (as benchresters do), or pushing back the shoulders .001-.002 with light-to-moderate charges should extend case life a bunch.

I saw those graphs on another site when they first come out. Only thing they point out is how many times those brands of cases can be reloaded until the case head separates. You ASSUME that neck sized only cases will last a lot longer, but nothing in that graph proves it. I'm just asking for some evidence to support your claim. It sounds plausible, but I want to see some proof that it's true. It also doesn't match what I've seen from experience. It should be a simple study to complete. Complete it using 100 cases out of the same bag and that would be statistically sufficient for me. I suspect the reason you won't find a study is because it will not matter. Other factors play a bigger role in case head separations than the way they are sized, the biggest one being pressure. Just like when the craze hit to only neck size for improved accuracy, now years later we find out that it doesn't matter.

You read this makes a difference and believe it, I don't. I'm just saying to keep an open mind and see if your experience matches it. I like my brass to last as long as possible, but in the end other issues normally consume it before the case head separates becomes an issue.

 

[sinister]

I concur. Experience with a loosy-goosy Remington factory neck and chamber will not be the same as fired in a custon tight-necked benchrest gun, chambered with new, custom chamber and finish reamers.

Benchresters (shooting custom 6PPCs) will have different case life experiences than someone shooting a factory Remington or Savage .243 (or a long range magnum).

Apples and oranges, to be sure. I don't have the money, desire, or interest to follow that rabbit. If my experience strictly with OEM and match guns can help someone (or not) it's only worth the electrons typed.

 

[kyshootnman]

Case overall length, as pointed out above, will always grow as the brass flows toward the case mouth (either from firing or re-sizing, especially full-length sizing -- the brass only has one direction to go/flow, and that's towards the case mouth).

Trimming the case back to minimum dimensions keeps the case within the boundaries of the chamber (the neck doesn't extend into the bore, "Pinching the bullet" and raising pressure).

Without an RCBS mic (as the OP pointed out) or some other device on your calipers (a Stoney Point or Hornday LNL, or some kind of comparator to consistently measure base-to-shoulder datum), how are you measuring?

Neck-sizing only/exclusively does not change the base-to-shoulder datum dimension or length, however the brass may eventually stick in the chamber and need an occasional full-length sizing to keep feeding and extraction easier. The frequency of how often you'll want to do it will vary by chamber pressure and brass hardness.

The first firing will determine the case's working length. If the brass had to stretch on the first shot the virgin brass will stretch-to-fit the chamber length. If it's a deep chamber then that's where first thinning will occur. Annealing will help with neck life later (as the neck is work-hardened), but may affect how much/far the the brass in the case walls and shoulder is worked on the fire-form.

The 142 SMK and the 140 A-Max are nominally the same length. The Sierra has a shorter bearing area and ogive. If seated to the same cartridge overall length as the A-Max it may touch the rifling leade sooner. In the OP's case, the bullet may jam into the lands sooner, spiking his pressure up a bit (in the Match King's favor it has a longer boat-tail which may also free up some case space. Add .1 grains more powder (as in his case) and pressures might (or might not) change (bullet seats earlier, plus more fuel).

Do you have a gage to check when your bullet ogives contact the leades, and then adjust from there for a touch fit, jam-fit, or free-jump?

Hodgdon's data states 41.5 to 44.5 of H4350, so your loads are well within min-max charges.

In the graphs I posted the case shoulders were DELIBERATELY pushed back .003-.005 to document case stretch to failure. Neck-sizing only (as benchresters do), or pushing back the shoulders .001-.002 with light-to-moderate charges should extend case life a bunch.

I'm not trying to argue, just stating that it can be done with the Wilson gage. The case is trimmed back, then the measurement is taken so the neck is not protruding from the gage, so an accurate measurement can be taken. Have you personally used a Wilson gage? I realize that separate bullets have different OAL to get the lands. I do have a gage I personally made one that uses a fired case from each of my chambers to measure to the lands. If you're using a gage with a standard brass, such as Hornday, your measurement isn't exact. The brass isn't formed to the headspace of your chamber. I have a handle on the basics of reloading as my 260 is shooting sub 1/2 moa. The original question was simply what was causing the ring, and most suggestions do not comply with what evidence I have provided.

 

[Edo1]

It's going to happen, only way to stop it is to not shoot it. What you are reading are opinions on how to slow down the process. One thing I think most agree on is that the the hotter the load, the faster it's going to occur. It's a cumulative process and there is no way to reverse it. Find a lower pressure load your gun likes and that will prolong your brass. The trade off to that is that you will need to use a heavier charge of powder.